This invention relates to a switch mode power supply suitable for the ignition and operation of a high-pressure discharge lamp comprising
switching means, induction means, capacitive buffer means and rectifying means for producing from an input voltage a current for the lamp by switching the switching means alternately to the conducting and to the non-conducting state, and PA1 a control circuit for supplying a switching signal comprising a switching-on signal for switching the switching means to the conducting state and a switching-off signal for switching the switching means to the non-conducting state.
Such a switch mode power supply is known from GB-2,102,641. The switching signal is produced in the control circuit by a separate oscillator. In order to obtain a supply of current to the lamp as constant as possible, the known switch mode power supply is provided with circuit means for the detection of the current through the switching means. The circuit means ensure that the current through the switching means is limited to a maximum value by interrupting the production of the switching signal as soon as the maximum current is detected. As a result, the switching means pass to the non-conducting state.
A disadvantage of the known switch mode power supply is that both current detection means and a separate oscillator are required. Thus, the construction of the switch mode power supply becomes fairly complex. The invention has for its object, inter alia, to provide a comparatively simple construction for a switch mode power supply while still limiting the current supply to the lamp.